Pilot Study of Proposed Revisions to Specifications for Hydraulic Cement Concrete

About the report:

This report summarizes the results of a pilot study of the statistical acceptance procedures proposed for adoption by the Virginia Department of Highways and Transportation. The proposed procedures were recommended in the report titled "Improved Specifications for Hydraulic Cement Concrete" and issued in 1983. This study revealed that practical difficulties would likely be encountered if the initially proposed revisions were adopted. Major problems were noted with the proposed system of random sampling based on a predetermined truckload of material, the definition of the total concrete placed on the contract as a single lot, the initially proposed requirement for average entrained air content, and the present practice of accepting concrete on the basis of it having 85% of the required 28-day strength at 14 days. After study of the findings, a revised proposal has been made for introducing such concepts into the Department's specifications for hydraulic cement concrete. The proposal is that a day's production of hydraulic cement concrete be considered a lot and that three samples per lot normally be taken for judging acceptability. The proper parameters for judging acceptance are based on a computerized statistical program (non-central-t) developed by the New Jersey Department of Transportation. These are discussed in the report and are recommended for adoption by the Virginia Department of Highways and Transportation. Where conditions warrant, a larger number of samples per day may be required with consequent reductions in the risks of accepting poor concrete.

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